1. Field of the Invention
This invention relates to a system for closing and opening to control with precision a flow of fluid, either gases and/or liquids, or finely divided loose materials. The invention relates in particular to a closing system having a closure member capable of withstanding relatively high pressures, and displaceable across the opening without imparting friction to surrounding sealing areas.
2. Description of Related Art
A gate wall is usually understood to include a closure member generally rectangular, a frame surrounding an opening, in which the closure member is disposed to slide therein and sealing strips are provided between the closure member and the frame. Major problems encountered with this type of construction are generally related to the absence of control regarding the compression of the closure member on its seat, since only the pressure or mass of the fluid acts on the closure member. Also, the friction exerted on the seal, results in seal wearing, deformation and leakages. Generally, leakage is controllable on the base portion of the seal; tightness being increased by increasing the vertical pressure exerted on the closure member. However, for the lateral sections, vertical pressure has no influence on the tightness of the lateral seals. This leakage problem is even more acute in the upper portion of the seal. Due to the sliding movement of the closure member, it is impossible to use sandwich seal strips.
In positive pressure situation, when the pressure is pushing a closure member against the opening, this type of construction is acceptable. However, when the pressure is negative, as the closure member moves away from the opening, serious leakage problems are encountered with the lateral and upper seals.
Also, in high negative pressure situations, it is difficult to close the opening until pressure equalization is obtained on both sides of the gate, generally by releasing the pressure in the conduit.
In U.S. Pat. No. 3,337,178 dated Aug. 22, 1967, Gordon teaches a valve for finely divided dry particulate materials. The valve is positively closed by a movement toward and away from a valve seat by providing leaf springs. The valve is operated by changing the convexity of the springs. Reproducibility is a function of the springs, which are resilient. Also, on increasing of convexity of the leaf springs, an oblique displacement of the closing member is obtained. This non-axial motion produces friction of the closing member on the valve seat and thereby wearing, deformation and deterioration of the seal.
In U.S. Pat. No. 4,524,950 dated Jun. 25, 1985, Vitas et al teach improved lateral seals by modifying their position, proposing oblique fixing with truncated V-shape seals to take advantage of the vertical pressure on lateral seals.
In U.S. Pat. No. 4,738,432 dated Apr. 19, 1988, Gardner et al teach two part sealing strips of sandwich type, consisting of a resilient layer and a superimposed bearing portion arranged to limit the maximum compression of the resilient portion in closed position.
In U.S. Pat. No. 4,204,662 dated May 27, 1980, Reynolds teaches a valve wherein a negative pressure, exerted on the closure member, is converted on the peripheral seal in a positive pressure by using a fulcrum which is located closer to the periphery than to its center. However, this approach does not solve the sealing problem of the upper joints or seals when rectangular closure member is used. Also, it is impossible to slide the closure member when a negative pressure is exerted over it.
In U.S. Pat. No. 2,999,666 dated Sep. 12, 1961, Sjogren teaches a valve having a circular closure member pivotally mounted along its side to an arm fixed to a stem, whereby the stem actuates a closure member.
In U.S. Pat. No. 2,767,956 dated Oct. 23, 1956, Rubin teaches a deformable diaphragm for another type of valve.
In Canadian Patent 1,036,571 dated Aug. 15, 1978, Connor et al teach special sealing means for sliding valves.
In Canadian Patent 803,875 dated Jan. 14, 1969, Combes teaches a valve with variable gauge portions.